Form value count limit 1024 exceeded

I've got a form with 2500 elements. (Why not!?) (It's for doing bulk updates if you must know)

In line with the suggested code here I implemented a RequestFormSizeLimit attribute like so

using Microsoft.AspNetCore.Http.Features;
using Microsoft.AspNetCore.Mvc.Filters;
using System;

namespace YourApp.Models
	/// <summary>
	/// Filter to set size limits for request form data
	/// </summary>
	[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = false, Inherited = true)]
	public class RequestFormSizeLimitAttribute : Attribute, IAuthorizationFilter, IOrderedFilter
		private readonly FormOptions _formOptions;

		public RequestFormSizeLimitAttribute(int valueCountLimit)
			_formOptions = new FormOptions()
				ValueCountLimit = valueCountLimit

		public int Order { get; set; }

		public void OnAuthorization(AuthorizationFilterContext context)
			var features = context.HttpContext.Features;
			var formFeature = features.Get<IFormFeature>();

			if (formFeature == null || formFeature.Form == null)
				// Request form has not been read yet, so set the limits
				features.Set<IFormFeature>(new FormFeature(context.HttpContext.Request, _formOptions));

Then, on the relevant POST action, I can:

[RequestFormSizeLimit(valueCountLimit: 4000)]
public ActionResult BulkUpdate(UpdateDetails updateDetails)